What is the ruling on one who constantly and uncontrollably experiences mazhī discharge, and is it permissible for him to delay prayer or not attend Friday prayer because of it?

What you are suffering from is a medical condition known as سلس (incontinence). If the time for prayer comes, you must wash what has been affected by prostatic fluid (madhy) from the male organ and clothing, then protect yourself, perform ablution (wudu'), and pray. You are not required to do anything after that, even if you become certain of its exit. You should do this at the time of each prayer, and it is not permissible for you to delay the prayer. The Malikis hold that perpetual incontinence (sals) that persists for more than half the time does not nullify ablution, and one may pray as many obligatory and supererogatory prayers as one wishes, as long as their ablution is not nullified by an event other than the incontinence. This applies if one is unable to stop it; but if one is able to stop it, then it nullifies ablution absolutely. The time for treatment and marriage is excused. If it is difficult for you to wash your clothes that have been affected by prostatic fluid, then it is excused.